Complex electronic power distribution systems exist and are increasingly relied upon to operate within power plants and within various vehicles, such as aircraft, watercraft, and land-based vehicles. Many electronic components contained in the distribution systems are of a critical nature, whereby, it is preferred that functions performed by these components are continuously available as required. It is therefore desirable that these components do not malfunction or become inoperable. Malfunctioning of any of the components can result in a large-scale system malfunction, potential damage to a system, or potential injury to a system operator or occupant.
In order to avoid component and system malfunctioning, redundancy is typically designed into the systems such that when a malfunction does occur, a second or third device is available to continue performing the same or similar function as that of the malfunctioning component or system. Multiple power sources and multiple system components are commonly used to provide redundant power source and system component functions.
Referring now to FIG. 1, an example of a traditional majority redundant system 10 is shown. Multiple power sources 12 are directly coupled to and associated with multiple processing units 14 of a controller 16. Power direct current (DC)/DC converters 18 are coupled between the power sources 12 and the processing units 14. Outputs (not shown) from each processing unit 14 are monitored by the controller 16. When all components within the power distribution system 17 are operating appropriately, the values of each output are approximately equal. The controller 16 determines a majority output value, through use of a voter (not shown), representing approximately a value that is equal to a majority of the outputs, which is determined to be a correct or best response. For example, when two of the outputs are approximately equal, the majority output value is set equal to that of those two outputs.
Each power source 12, processing unit 14, and power converter 18 form a power distribution path or line 22. The distribution system 17 is thus, referred to as a triple redundant power system, since there are three possible power distribution paths.
The distribution system 17 is also a single-fault-tolerant system and as such is capable of withstanding a single line or power distribution path malfunction. In using the system 10, when one power source or converter is not operating appropriately, for example, when a malfunctioning line 24 is not operating appropriately, the remaining two power sources and corresponding converters or lines 26 may remain operating and provide proper power to the controller 16.
When line 24 malfunctions a best response can be determined from the remaining two lines 26. Unfortunately, when a second line is also malfunctioning, such as the one designated as line 28, a majority determination cannot be easily performed, since one may not be able to determine which of the remaining two lines 26 is correct and which is malfunctioning. The redundant system 10 is sometimes referred to as a R(2/3) system, defined as one where two out of three elements are required to provide appropriate outputs at terminal 20.
It is also desirable that power distribution systems isolate both power sources and critical electronic components or systems, sometimes referred to as loads. When a power distribution system does not have isolated power sources, ground current may flow through other undesirable return paths and jeopardize system operations and it also introduces an unsafe environment for system operators.
Thus, without redundancy a “single-point of failure” may occur, causing a critical electronic system to malfunction from, just a single component malfunction. Of course, single-point failures are not acceptable for critical electronic systems.
Although, the system of FIG. 1 provides the above desired redundant features of a power distribution system it has a large number of components, which cause the system to be heavy and costly to manufacture and operate, especially in aerospace applications.
Referring now also to FIG. 2, a traditional DC/DC converter 29, which is representative of the power converters 18 in FIG. 1, is shown. The converter 29 includes a main controller 30 that is coupled to multiple transformers T1, T2, and T3 for voltage conversion, isolation of input voltage at input terminal 31 from output voltage at output terminal 32, and isolation of multiple regulated feedback loops 33. An auxiliary regulator circuit 34 provides power to the controller 30. The converter 29 includes input filters 35, an inrush limiter 36, and other common circuitry known in the art. In operation the controller 30 monitors a reference voltage and the converter output voltage and current through the feedback loops 33 and adjusts voltage output of the converter 29 by adjusting energy flow across the third transformer T3. The controller 30 may activate or deactivate the converter 29 on command, allowing the system 10 to switch between power sources 12, processing units 14, and converters 18 or lines 22.
Each additional transformer downstream from a previous transformer, such as transformers T1 and T3 being downstream from transformer T2, tends to have voltage and/or current that is feedback to the controller 30 and crosses isolation boundaries 37 contained within the transformers T1, T2, and T3. The configuration of the converter 19 is complex and costly, especially due to the number of transformers that must be utilized for isolation of the feedback loops 33 and the presence of the auxiliary regulator circuit 34.
Referring now to FIG. 3, another example of a majority redundant power distribution system 38 utilizing “ORing” diodes 39 is shown. Two power sources 40 are utilized rather than three, as with the previous example, and are coupled to three processing units 41 of a controller 42. Diodes 39 are coupled between outputs 43 of a pair of power DC/DC converters 44 and input 45 of a center one 46 of the processing units 41. Diodes 39 are referred to as “ORing” diodes because they operate in a logical OR manner to provide power from either the one designated 48 or the other designated 50 of the power converters 44 to the center-processing unit 46. Thus, for example, when either power converter 48 or 50 is malfunctioning, the other or properly operating power converter supplies power to the center-processing unit 46 through diodes 39.
Although, the configuration of FIG. 3 provides a low cost and simple redundant power distribution system with fewer power converters relative to and unlike that of the system of FIG. 1, it also, unfortunately, has associated disadvantages and is a single-point of failure system. One disadvantage is that the diodes 39 inherently cause a drop in voltage between the sources 40 and the center-processing unit 46 that causes the processing units 46 to operate with an undesirable input voltage level, which can result in an erroneous voltage level at output 52. Another disadvantage with system 38 is that when the center-processing unit 46 is malfunctioning both converters 44 may become inoperable, such as in a situation when the processing unit 46 is shorted to ground. Additionally, system 38 is limited in its ability to switch between power sources 40, processing units 41, and converters 44; for example, processing unit 46 continuously receives power from either source 40 due to the ORing configuration. The above associated disadvantages are also true when multiple sets of ORing diodes are utilized.
It is therefore desirable to provide a redundant power distribution system that does not exhibit the above stated disadvantages and that provides reliability at a level that is at least equal to that of a triple redundant system, that provides separate lines of regulated and isolated output power, and that minimizes number of system components, weight, and costs involved therein.